No. 10/May 29, 1998
Seedling Blight Problems Continue in Corn
Wet soil conditions are continuing to cause seedling blight problems in corn. The primary pathogen involved appears to be the fungus Pythium, which is favored by wet soils and cool weather. Pythium infections are most common in very wet or flooded areas of fields. Symptoms on plants include a general browning of the seminal, or primary, root tips or of the hypocotyl, as well as poor plant vigor. Infected plants usually do not recover unless there are adequate permanent roots to replace those damaged by the fungus.
As far as replant decisions are concerned, corn producers have a few options when dealing with seedling blights. Almost all of the commercial seed is now treated with a fungicide to protect against Pythium. The fungicide may be Allegiance, Apron XL, or Apron--all of which should provide equal measures of protection against Pythium. However, this year, some producers have asked if the level of fungicide was adequate to protect seedlings due to the prolonged delays in germination for some fields of corn. In fields where germination did not occur for 10 or more days, the levels of protection offered by the seed treatments may not have been affected by the high soil-moisture level or the delayed germination and seedling emergence. Seed treatments are designed to provide 10 to 14 days of protection under "normal" conditions (whatever you consider that to be in the Midwest) when germination would be expected to occur within a few days to 1 week after planting. When rains and cool weather continue, the effectiveness of the fungicide can be compromised and seedling blights can be seen. Such was the case this year in many areas of the state.
One of two other fungicides will be applied to corn in addition to the Pythium-control material. Depending on the seed company, either Maxim or Captan will be applied. Both products provide a broad-spectrum approach to fungal disease management and should protect seed against soil-borne fungi. Some questions have been asked as to which material is most effective in wet soils. Currently, there are no published data from replicated trials to favor either product. Therefore, producers should not become overly concerned about performance of hybrid seed based upon the selection of a seed treatment by a company. Seedling blight fungi are affected by many factors beyond the seed treatment itself.H. Walker Kirby (firstname.lastname@example.org), Extension Plant Pathology, (217)333-8414